Why is my IP blacklisted, and how do I get it removed?

An IP blacklist (the operators prefer blocklist, or DNSBL for DNS-based blocklist) is a published list of addresses that have been seen doing something unwanted: sending spam to trap addresses, hosting an open relay or proxy, scanning other people's servers, or talking to a botnet controller. Mail servers consult these lists before accepting a message, and increasingly so do web firewalls, login systems and fraud scorers.

There are dozens of lists with different purposes and different standards of evidence. Three distinctions matter when you read a result:

• Per-address vs per-range. Most lists name single addresses. Some, such as UCEPROTECT levels 2 and 3 and the Spamhaus SBL, list entire provider ranges or networks because of a neighbor's behavior. You cannot fix those yourself.
• Behavioral vs policy. Behavioral lists react to observed abuse. Policy lists, such as the Spamhaus PBL, simply record that a range is residential and should not be sending mail directly; being on one is normal for a home connection and only matters if you run a mail server.
• Who uses the list. Spamhaus ZEN and Microsoft's internal lists block mail at a large share of the world's mailboxes; a listing on a small aggressive list may affect almost nobody.

Run the IP blacklist check. It queries ten public blocklists in parallel for your current address, or any address you enter, and shows for each one whether it answered listed, what the return code means, when it was checked and where to request removal. UCEPROTECT levels 2 and 3 are marked informational because they describe your provider's range rather than you.

Two lists are not in that set and need a direct visit: Spamhaus, whose public data cannot be queried from shared services under its terms, has a free lookup at check.spamhaus.org that also detects your own address automatically; and Microsoft, which publishes no list at all and reveals a block only in the bounce message. So always read the bounce. The line beginning 550 names the list or service that refused the mail, and that is the one to fix first. The IP fraud score shows how the same address looks to websites rather than mail servers, with each contributing signal spelled out.

Malware or a compromised device on your network

The most frequent cause for a home or office address. An infected PC, a camera with a default password or a hijacked router sends spam or scans the internet in the background, and the lists notice within hours. The listing describes the device, not you, but it is your address.

A compromised email account or web form

On a mail server, one stolen password or one contact form without rate limiting can send tens of thousands of messages overnight. Spam-trap hits follow, then SpamCop and Spamhaus CSS listings.

An open relay or open proxy

A mail server that accepts and forwards mail from anyone, or a proxy with no authentication, gets found by scanners within a day and listed on the proxy and abuse lists (DroneBL and others) shortly after.

Shared and dynamic addresses carrying someone else's history

If your ISP hands out dynamic addresses, today's address was someone else's last week. Behind carrier-grade NAT you share one public address with thousands of strangers right now, and one of them running a bot is enough. VPN exits and shared web hosting work the same way: the address's reputation is the sum of everyone on it.

Sending bulk mail badly

Legitimate newsletters to stale lists hit spam traps too. Old addresses are recycled into traps by the list operators precisely to catch senders who never clean their lists.

Policy, not behavior

A residential address on the Spamhaus PBL has done nothing wrong; the list records that the range is not supposed to send mail directly. The fix is to send through your provider's or a third party's mail server, not to request removal.

Fix the cause first. Operators see repeat listings, and several will refuse or slow a second removal. Then work through the lists named in your bounces and in the checker result:

1. Spamhaus (SBL, XBL, CSS, PBL, combined as ZEN). Look the address up at check.spamhaus.org; the result explains the reason and opens a removal request when one is possible. XBL and CSS listings (compromised device, spam source) can be requested for removal once the device is clean; one request covers both. PBL listings are removed only if you genuinely run a mail server on that address. SBL listings cover a network and are removed only at the request of the provider's abuse team, so contact your ISP or host and ask them to handle it; other Spamhaus removals wait until the SBL entry is cleared.
2. Microsoft (Outlook.com, Hotmail, Microsoft 365). A bounce containing 5.7.606 through 5.7.649 (banned sending IP) is handled at the delist portal, sender.office.com: enter the recipient address from the bounce and the blocked IP, confirm the verification email, then choose Delist IP. Expect up to 24 hours or more. A bounce with 5.7.511 (banned sender) cannot use the portal; forward the full bounce to delist@microsoft.com and expect a reply within about 48 hours.
3. SpamCop. No form. A listing expires automatically 24 hours after the last spam report, and the lookup page shows the countdown; after it reaches zero, allow up to four hours for the change to reach the mirrors. SpamCop asks that you not request early removal, even after fixing the problem.
4. Barracuda Reputation Block List. Submit the removal request form on barracudacentral.org with the server address, a contact email, phone number and a short explanation of what you fixed. Requests with a valid explanation are typically processed within 12 hours; blank or repeated requests are ignored.
5. UCEPROTECT level 1. Expires on its own 7 days after the last message hits their traps. Levels 2 and 3 list your provider's range or network and cannot be removed by you; they are rarely used by large receivers, so note them and move on.
6. PSBL, DroneBL, blocklist.de and the smaller lists. PSBL offers immediate self-service removal from its lookup page. DroneBL expects the proxy or bot to be closed before you request removal through its lookup. blocklist.de has a removal form for addresses that have stopped attacking. The checker links each list's page beside its result.

In every request, give the address, the date you fixed the problem and what it was. Vague requests are the ones that get ignored.

• Monitor. Re-run the blacklist check weekly for every address that sends mail, and whenever bounces start. Catching a listing on day one is the difference between a nuisance and a week of lost mail.
• Authenticate your mail. Publish SPF, DKIM and a DMARC policy for your domains; check the records with the DNS lookup tool. This stops others from sending as you and is now required by Google and Yahoo for bulk senders.
• Set reverse DNS. A sending server whose address resolves to a hostname that resolves back to the same address is treated far more kindly; the reverse DNS lookup shows what yours says.
• Rate-limit and alert. Cap outbound mail per account per hour and alert on spikes, so a stolen password cannot send thousands of messages before you notice.
• Patch and lock down. Update routers, cameras and web applications, change default passwords, and close relays and proxies you do not need. The port checker shows which services on your address are reachable from outside.
• Separate streams. Send marketing mail from a dedicated address or a reputable delivery service so one bad campaign cannot block your invoices and password resets.
• Change address as a last resort. A home address that keeps returning to lists through no fault of yours can be replaced by asking the provider for a new one; some ranges carry a reputation that outlives every cleanup.